Tissue graft compositions made of devitalized native tissues have been widely used to repair or restore damaged, deformed, or missing tissues in patients. Typically these compositions are made from the extracellular matrix of tissues, for example, the submucosa of the intestine (SIS), or urinary bladder (UBS), and the epithelial basement membrane of, for example, the urinary bladder (UBM). Collectively these compositions are termed extracellular matrices or ECMs, SIS, UBS, and UBM are further described in U.S. Pat. Nos. 6,576,265, 6,579,538, 5,573,784, 5,554,389, 4,956,178, and 4,902,508, each of which are incorporated by reference herein.
Briefly, SIS and UBS are made from gastrointestinal tissue and urinary bladder, respectively, by delaminating the submucosa from all other layers of the tissue source and retaining the submucosa to form a tissue graft composition. UBM is made by delaminating the epithelial basement membrane and, optionally, delaminating one or more of the deeper layers from the epithelial cells of the urinary bladder and retaining at least the epithelial basement membrane to form a tissue graft composition. Other tissues including, but not limited to skin and tissues of the gastrointestinal tract, e.g., esophagus, stomach, and intestine, may also be used to make an ECM including epithelial basement membrane by delaminating the epithelial basement membrane from the epithelial cells and, optionally, one or more of the deeper layers of the tissue source. Still other native ECMs may be made from connective tissues such as aponeurosis, tendon, ligament, smooth and skeletal muscle, and treatment-site specific ECMs.
ECMs are used to restore, for example, epithelial tissues. Restoration of epithelial tissues requires restoration of the epithelium and the connective tissue elements underlying the epithelial tissue. Epithelial restoration occurs rapidly when epithelial basement membrane is present. However, restoration of the connective tissue elements is slower than epithelial tissue restoration, prolonging the complete restoration of damaged epithelial tissues.
Each of the ECMs, such as UBS, UBM, and SIS, known in the prior art, are resorbed at the site of implantation in a patient. For example, a single sheet of urinary bladder matrix (UBM) may resorb, for example, within a week when implanted in a topical wound. FIGS. 1A-C depict the rapid resorption profile of a prior art ECM material 12 implanted at a tissue site 10 in a patient. FIG. 1A shows the sheet of ECM 12 on day 0 of implantation. As shown, the ECM 12 fills the entire tissue site 10. At day X after implantation, FIG. 1B shows that the ECM 12 has been partially resorbed at the tissue site 10 as shown by the reduced surface area of the ECM 12 as compared to the surface area of the ECM 12 in FIG. 1A. At day Y after implantation, FIG. 1C shows that the ECM 12 has been completely resorbed by the tissue site 10 as no ECM 12 remains.